Note 10 - Commitments and Contingencies (Details Textual) $ in Millions	3 Months Ended
	Dec. 31, 2022 USD ($)
Long-Term Purchase Commitment, Amount	$ 1,445.0
Capital Committed to Contribute to Partnership	10.0
Contributed Capital, Total	1.9
Spire Missouri [Member]
Long-Term Purchase Commitment, Amount	1,027.3
Spire Alabama Inc [Member]
Long-Term Purchase Commitment, Amount	$ 244.6